ALPO COMET NEWS FOR SEPTEMBER 2024
A Publication of the Comets Section of the Association of Lunar and Planetary Observers
By Carl Hergenrother
The monthly Association of Lunar and Planetary Observers (ALPO) Comet News PDF can be found on the ALPO Comets Section website @ http://alpo-astr....org/Comets/ and in the Comets Section Image Gallery. A shorter version of this report is posted here (minus the magnitude estimates, images, and other figures contained in the full PDF). The ALPO Comets Section welcomes all comet-related observations, whether textual descriptions, images, drawings, magnitude estimates, or spectra. You do not have to be a member of ALPO to submit material, though membership is encouraged. To learn more about the ALPO, please visit us @ http://alpo-astronomy.org. We can also be reached at < comets @ alpo-astronomy.org >.
Summary
The stage is set for C/2023 A3 (Tsuchinshan-ATLAS), which will arrive at the perihelion on September 27. In August, the comet continued to slowly brighten, but otherwise, it looked healthy. The STEREO-A spacecraft took the last observations on August 21, with the comet now too close to the Sun to be observed.
Assuming the comet continues to brighten and not disintegrate, it should become observable again during the second half of September, at least for those clear, unobstructed eastern morning horizons. The comet will be competing with a rapidly brightening dawn sky. It should be within range of imagers, but will it be bright enough for visual observations?
The real show will be in October, when the comet may become a short-lived daylight comet from October 8 to 10 and then a nice evening object starting around October 13.
Two other comets are expected to be brighter than 12th magnitude in September. 13P/Olbers is a northern hemisphere object fading from 8th to 9th magnitude in the evening sky. 12P/Pons-Brooks is a southern hemisphere object fading from 10-11th magnitude, also in the evening sky.
Last month, the ALPO Comets Section received 103 images and 167 magnitude estimates of 22 comets: C/2023 V4 (Camarasa-Duszanowicz), C/2023 C2 (ATLAS), C/2023 A3 (Tsuchinshan-ATLAS), C/2022 N2 (PANSTARRS), C/2021 S3 (PANSTARRS), C/2021 G2 (ATLAS), C/2020 V2 (ZTF), C/2020 K1 (PANSTARRS), P/2010 WK (LINEAR), 328P/LONEOS-Tucker, 305P/Skiff, 302P/Lemmon-PANSTARRS, 146P/Shoemaker-Levy, 136P/Mueller, 133P/Elst-Pizarro, 130P/McNaught-Hughes, 125P/Spacewatch, 89P/Russell, 54P/de Vico-Swift-NEAT, 37P/Forbes, 13P/Olbers, and 12P/Pons-Brooks.
A big thanks to our recent contributors: Dan Bartlett, José J. Chambó, Michel Deconinck, Jose Guilherme de Souza Aguiar, Juan Jose Gonzalez Suarez, Christian Harder, Eliot Herman, Michael Jäger, John Maikner, Gianluca Masi, Michael Mattiazzo, Martin Mobberley, Mike Olason, Andrew Pearce, Chris Schur, and Christopher Wyatt.
Request for Observations
As always, the Comet Section is happy to receive all comet observations, whether textual descriptions, images, drawings, magnitude estimates, or spectra. Please send your observations via email to the Comets Section < comets @ alpo-astronomy . org >, Comets Section Coordinator Carl Hergenrother < carl.hergenrother @ alpo-astronomy . org > and/or Comets Section Acting Assistant Coordinator Michel Deconinck < michel.deconinck @ alpo-astronomy . org >.
Photometric Corrections to Magnitude Measurements
We include lightcurves for the comets discussed in these reports and apply aperture and personal corrections to the visual observations and only personal corrections to digital observations. Though we try to keep these lightcurves up to date, observations submitted in the days before publication may not be included in the lightcurves until next month’s News. All magnitude estimates are affected by many factors, including instrumental (aperture, focal length, magnification, type of optics), environmental (sky brightness due to moonlight, light pollution, twilight, aurora activity, zodiacal light, etc.), cometary (degree of condensation, coma color, strength and type of gas emission lines, coma-tail interface) and personal (sensitivity to different wavelengths, personal technique, observational biases). The first correction used here corrects for differences in aperture [Charles S. Morris, On Aperture Corrections for Comet Magnitude Estimates. Publ Astron Soc Pac 85, 470, 1973]. Visual observations are corrected to a standard aperture of 6.78 cm by 0.019 magnitudes per centimeter for reflectors and 0.066 magnitudes per centimeter for refractors. After applying the aperture correction and if a sufficient number of visual observations are submitted for a particular comet, we also determine personal corrections for each observer for each comet; for digital observations, only a personal correction is applied. A single observer submitting both visual and digital magnitude measurements may also have separate corrections for each observing method. If the magnitudes shown in the text don’t match those plotted in the lightcurves, it is because of the application of these corrections.
Acknowledgments
In addition to observations submitted directly to the ALPO, we occasionally use data from other sources to augment our analysis. Therefore, we acknowledge with thanks observations submitted directly to the ALPO and those submitted initially to the International Comet Quarterly, Minor Planet Center, and COBS Comet Observation Database. In particular, we have been using observations submitted to the COBS site by Thomas Lehmann for our analysis and would like to thank Thomas for his COBS observations. We would also like to thank the Jet Propulsion Laboratory for making their Small-Body Browser and Orbit Visualizer available and Seiichi Yoshida for his Comets for Windows programs that produced the lightcurves and orbit diagrams in these pages. Last but not least, we’d like to thank Syuichi Nakano and the Minor Planet Center for their comet orbit elements, the asteroid surveys and dedicated comet hunters for their discoveries, and all of the observers who volunteer their time to add to our knowledge of these fantastic objects.
Thank you to everyone who contributed to the ALPO Comets Section!
Clear skies!
- Carl Hergenrother
Comets Calendar
Lunar Phases (UTC)
Sep 03 - New Moon
Sep 11 - First Quarter Moon
Sep 18 - Full Moon
Sep 24 - Last Quarter Moon
Comets at Perihelion
Sep 03 - 54P/de Vico-Swift-NEAT [q = 2.17 au, 7.4-yr period, V ~ 18, visual discovery by de Vico in 1844 (q = 1.19 au), visual re-discovery by Swift in 1894 (q = 1.39 au), photographic recovery by Klemola in 1965 (q = 1.62 au), CCD re-discovery by NEAT in 2002 (q = 2.14 au), also seen at 2009 return, missed at 2017 return, seen at 6 returns and missed at 23 returns since discovery]
Sep 06 - P/2014 MG4 = 2024 K2 (Spacewatch-PANSTARRS) [q = 3.72 au, 11.2-yr period, V ~ 19-20, discovered in 2014, 2024 is 2nd observed return]
Sep 06 - C/2024 G5 (Leonard) [q = 2.95 au, V ~ 19]
Sep 09 - C/2021 G2 (ATLAS) [q = 4.98 au, V ~ 13-14]
Sep 14 - C/2022 E2 (ATLAS) [q = 3.67 au, V ~ 11-12]
Sep 16 - C/2023 TD22 (Lemmon) [q = 2.36 au, V ~ 16]
Sep 19 - 384P/Kowalski [q = 1.11 au, 4.9-yr period, V ~ 18, discovered in 2014, seen at 2019 return, 3 observed returns]
Sep 27 - C/2023 A3 (Tsuchinshan-ATLAS) [q = 0.39 au, see much more below]
Sep 28 - P/2019 M2 = 2024 C6 (ATLAS) [q = 1.07 au, 5.3-yr period, V ~ 20, discovered in 2019, passed 1.06 au from Earth in 2019, the current return is similar with an approach to 1.07 au of Earth, low activity short-period comet observed at 2 returns]
Photo Opportunities
Sep 01 - 13P/Olbers within a degree or so of the bright globular cluster pair M53 and NGC 5053
Sep 22-23 - 12P/Pons-Brooks passes over the bright Omega Centauri (NGC 5139) globular cluster!
Sep 30 - 13P/Olbers passes within 20’ of 10th mag galaxy NGC 5701
Comets News
Looking Ahead to the Next 12 Months
The chart below shows those comets expected to become brighter than magnitude 10 in 2024. The number in each date bin is the expected brightness for that date. Magnitudes are only shown for dates when the comet is above the horizon during the dark of night (between the end of astronomical twilight in the evening and the start of astronomical twilight in the morning). The only exceptions are the dates bolded in red for C/2023 A3 (Tsuchinshan-ATLAS) and C/2024 G3 (ATLAS), when the comets will only be above the horizon in bright twilight but may still be bright enough to be observed.
All brightness predictions are just that—predictions and may be off by many magnitudes.
Last 10 Periodic Comet Numberings (from WGSBN Bull. 4, #11)
486P/2018 L5 = P/2024 H1 (Leonard) MPC 174198
485P/2022 U6 = P/2006 AH2 (Sheppard-Tholen) MPC 172941
484P/2005 XR132 (Spacewatch) MPC 172941
483P/2016 J1 = P/2010 M9 = P/2020 Y6 = P/2021 K5 (PANSTARRS) MPC 171409
482P/2014 VF40 (PANSTARRS) MPC 171409
481P/2012 WA_34 = P/2024 C5 (Lemmon-PANSTARRS) MPC 171409
480P/2014 A3 = P/2023 X6 (PANSTARRS) MPC 169139
479P/2011 NO1 = P/2023 WM26 (Elenin) MPC 169139
478P/2023 Y3 = P/2017 BQ100 (ATLAS) MPC 169139
477P/2018 P3 = P/2023 V8 (PANSTARRS) MPC 169139
New Recoveries & Discoveries
P/2024 Q1 (PANSTARRS) - The Pan-STARRS asteroid survey found this 20th magnitude comet on 2024 August 27 with one of their 1.8-m reflectors at Haleakala. P/2024 Q1 is a short-period comet with a 6.6-year orbital period. Perihelion was on 2024 June 14, at 1.64 au. The comet is now fading. [CBET 5437, MPEC 2024-Q87]
P/2024 O3 = P/2010 WK = P/2010 PB_57 (LINEAR) – The "Zwicky Transient Facility" (ZTF) picked up an apparently asteroidal object in July and August at 19th magnitude. The object was identified as the returning short-period comet P/2010 WK (LINEAR). It was also linked with the apparent asteroid 2010 PB57. Perihelion was on 2024 July 20, at 1.78 au. Currently, P/2024 O3 is roughly 3 magnitudes fainter in absolute brightness than it was in 2010. With perihelion in July, the comet should now fade. With a 13-year orbital period, it’ll return to perihelion in April 2038. [CBET 5436, MPEC 2024-Q34]
P/2024 O2 (PANSTARRS) – The Pan-STARRS1 1.8-m reflector at Haleakala discovered a 20-21st magnitude short-period comet on 2024 July 28. Pan-STARRS pre-discovery observations were found from 2024 June 30. P/2024 O2 should now fade after its 2024 April 19 perihelion at 3.70 au. The comet has a 20-year orbital period. [CBET 5428, MPEC 2024-P90]
P/2024 N6 = P/2002 QU151 (NEAT-PANSTARRS) – This short-period comet was discovered in 2012 by amateur astronomer Reinder J. Bouma in archival NEAT observations from 2002. Since the object’s cometary appearance was “borderline” in the 3 nights of observations from 2002, it wasn’t designated as a comet but rather as an asteroid, 2002 QU151. The Pan-STARRS survey serendipitously re-discovered the object as a comet on 2024 July 9 at 20th magnitude with their Pan-STARRS2 1.8-m reflector at Haleakala. Like the previous two discoveries above, P/2024 N6 has passed its perihelion and fading [T = 2024 May 19 at 1.68 au]. With a 7-year orbital period, its next perihelion will be in December 2031. [CBET 5427, MPEC 2024-P41]
P/2024 K2 = P/2014 MG4 (Spacewatch-PANSTARRS) – Rob Weryk reported the recovery of P/2014 MG4 (Spacewatch-PANSTARRS) by the Pan-STARRS1 1.8-m in April and May 2024 images at 21st magnitude. Perihelion will be on 2024 September 6, at 3.72 au, with the comet peaking at 20th magnitude next July. S. Nakano reports in CBET 5431 that the comet passed 0.05 au from Jupiter in 1955. Before close approach with Jupiter, the comet was on a 44.8-year orbit with a perihelion at 5.29 au. The comet’s current orbit has an orbital period of 11.2 years. [CBET 5431, MPEC 2024-Q26]
P/2024 C6 = P/2019 M2 (ATLAS) - Rob Weryk also reported the recovery of P/2019 M2 (ATLAS) on images taken by the Pan-STARRS1 and 2 telescopes in February, March, and April of 2024. Though it has a relatively small perihelion distance of 1.07 au (on 2024 September 28), it also appears to be a very low-activity comet and is not expected to become brighter than 20th magnitude. In 2019, it approached to 0.21 au of the Earth but never got brighter than 17-18th magnitude and displayed a very weak coma and tail. With a 5.3-year orbital period, it will be next at perihelion in January 2030. [CBET 5433, MPEC 2024-Q25]
C/2023 TD22 (Lemmon) – The Mount Lemmon Survey used their 1.5-m telescope to discover this apparently asteroidal object on 2023 October 12 at 20th magnitude. Recent observations have found cometary activity resulting in its redesignation as a comet. C/2023 TD22 (Lemmon) is a long-period comet with an orbital period of 334 years. It is currently peaking at 16th magnitude as it approaches a 2024 September 16 perihelion at 2.36 au. [CBET 5429, MPEC 2024-P107]
P/2023 JN16 (Lemmon) – Another apparently asteroidal Mount Lemmon discovery from 2023 has been observed to be active. Discovered on 2023 May 10 at 19th magnitude, P/2023 JN16 is a Main Belt comet or activated asteroid. The recognition of P/2023 JN16 as a comet resulted from a collaboration due to the effort of amateur astronomers on the Minor Planet Mailing List.
On June 1, Peter VanWylen wrote, “I'm not sure if anyone else is looking into 2023 JN16, but it's very bright to have been missed all this time and just now be discovered in 2023. It should be brighter than magnitude 22 every day of the year for many decades (regularly reaching magnitude 18) and was only just discovered. I think there's a real chance it's active or in outburst.”
In response to Peter’s post, observers identified a cometary activity in images taken between June 2023 and June 2024. Interestingly, the ZTF survey reported that the object was detected in images taken on 2023 April 29 but not in images taken on April 27 or earlier, suggesting an outburst, impact, or break-up event between those dates.
The object is on a typical Main Belt orbit with an orbital period of 4.4 years, perihelion at 2.30 au, semi-major axis of 2.70 au, and inclination of 3.7 degrees. [CBET 5430, MPEC 2024-Q04]
Comets Brighter than Magnitude 6
C/2023 A3 (Tsuchinshan-ATLAS)
Discovered on 2023 January 9 at the Purple Mountain Observatory's XuYi Station and on February 22 by ATLAS
Dynamically new long-period comet
Orbit (from Minor Planet Center, MPEC 2024-P125)
C/2023 A3 (Tsuchinshan-ATLAS)
Epoch 2024 Oct. 17.0 TT = JDT 2460600.5
T 2024 Sept. 27.74083 TT Rudenko
q 0.3914103 (2000.0) P Q
z -0.0002358 Peri. 308.49352 +0.36145497 +0.90082653
+/-0.0000004 Node 21.55948 +0.91852494 -0.29970120
e 1.0000923 Incl. 139.11044 -0.16019439 +0.31415084
From 4947 observations 2022 Apr. 9-2024 Aug. 2, mean residual 0".4.
1/a(orig) = +0.000005 AU**-1, 1/a(fut) = -0.000036 AU**-1.
Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)
C/2023 A3 (Tsuchinshan-ATLAS) Max El
(deg)
Ast Twi Nau Twi
Date R.A. Decl. r d Elong Ph.Ang. Const Mag 40N 40S 40N 40S
2024-Sep-01 10 43 -03 17 0.781 1.743 11E 15 Sext 6.5 -25 -9 -19 -3
2024-Sep-06 10 41 -04 01 0.684 1.642 11M 17 Sext 6.0 -21 -7 -15 -1
2024-Sep-11 10 38 -04 44 0.589 1.519 13M 23 Sext 5.5 -17 -4 -10 2
2024-Sep-16 10 36 -05 24 0.502 1.370 16M 35 Sext 5.0 -12 -1 -5 5
2024-Sep-21 10 35 -05 55 0.432 1.191 20M 54 Sext 4.3 -7 1 -1 7
2024-Sep-26 10 42 -06 06 0.394 0.983 22M 81 Sext 3.4 -4 2 2 8
2024-Oct-01 11 04 -05 44 0.402 0.767 21M 114 Leo 2.2 -4 -1 2 5
2024-Oct-06 11 57 -04 31 0.451 0.581 12M 150 Vir -0.2 -9 -10 -3 -4
Comet Magnitude Formula (from ALPO, COBS, and MPC data)
m1 = -16.6 + 5 log d + 35.0 log r [Through T-650 days]
m1 = 0.2 + 5 log d + 15.7 log r [Between T-650 and T-300 days]
m1 = 6.0 + 5 log d + 6.6 log r [Between T-300 days and perihelion]
m1 = 7.4 + 5 log d + 10.0 log r [After perihelion, assumed]
where “t” is the date of perihelion, “d” is Comet-Earth distance in au, and “r” is Comet-Sun distance in au
Like with Mark Twain, the reports of C/2023 A3 (Tsuchinshan-ATLAS)’s demise have been greatly exaggerated. At least until August 21, when the last observations were made, Tsuchinshan-ATLAS was still going strong.
Most northern hemisphere observers lost sight of the comet in July, while southern hemisphere observations continued through August 12. The STEREO-A spacecraft also observed the comet between August 1 and 21.
So, for now, the comet looks healthy and displays a dust and gas tail. The following predictions assume it will continue to brighten at its recent rate, a relatively slow 6.6 log r. We will also assume that it will survive perihelion, which is always a question mark for dynamically new comets (assuming that the comet is dynamically new).
September sees Tsuchinshan-ATLAS start the month at a small solar elongation of 11 degrees, 0.78 au from the Sun, and 1.74 au from Earth. On the 27th, it arrives at perihelion at 0.39 au from the Sun, 0.91 au from Earth, but a solar elongation of 23 degrees.
The following table expands on the one above and shows the comet's altitude at the start of astronomical and nautical twilight in the morning sky from +40 and -40 degrees latitude. It highlights how difficult it will be to observe Tsuchinshan-ATLAS in September, especially from the northern hemisphere. One will need a clear sky with a flat, unobstructed morning eastern horizon. The magnitude predictions include enhanced brightness due to the forward scattering of dust at large-phase angles.
Max El
(deg)
40S 40N
Date Nau Twi Ast Twi Nau Twi Ast Twi r delta Elong Ph.Ang. Mag
2024-Sep-09 1 0.63 1.57 12 20 5.7
2024-Sep-10 1 0.61 1.55 12 21 5.6
2024-Sep-11 2 0.59 1.52 13 23 5.5
2024-Sep-12 2 0.57 1.49 14 25 5.4
2024-Sep-13 3 0.55 1.46 14 27 5.3
2024-Sep-14 4 0.54 1.43 15 30 5.2
2024-Sep-15 4 0.52 1.40 16 32 5.1
2024-Sep-16 5 0.50 1.37 16 35 5.0
2024-Sep-17 5 0.49 1.34 17 38 4.8
2024-Sep-18 6 0.47 1.30 18 42 4.7
2024-Sep-19 6 0.46 1.27 19 46 4.6
2024-Sep-20 7 1 0.44 1.23 19 50 4.5
2024-Sep-21 7 1 0.43 1.19 20 54 4.3
2024-Sep-22 7 1 0.42 1.15 21 59 4.2
2024-Sep-23 8 2 0.41 1.11 21 64 4.0
2024-Sep-24 8 2 1 0.41 1.07 22 69 3.8
2024-Sep-25 8 2 2 0.40 1.03 22 75 3.6
2024-Sep-26 8 2 2 0.39 0.98 22 81 3.4
2024-Sep-27 8 2 2 0.39 0.94 22 87 3.2
2024-Sep-28 7 1 3 0.39 0.90 22 93 3.0
2024-Sep-29 7 1 3 0.39 0.85 22 100 2.7
2024-Sep-30 6 3 0.40 0.81 22 107 2.5
2024-Oct-01 5 2 0.40 0.77 21 114 2.2
2024-Oct-02 4 2 0.41 0.73 20 121 1.9
2024-Oct-03 2 1 0.42 0.69 19 128 1.5
2024-Oct-04 1 0.43 0.65 17 135 1.0
September 1 [0.78 au from the Sun, 1.74 au from Earth, 11 deg solar elongation, 15 deg phase angle]
Tsuchinshan-ATLAS is at magnitude 6.5 but too faint and close to the Sun to be observed from the ground.
September 14 [0.54 au from the Sun, 1.43 au from Earth, 15 deg solar elongation, 30 deg phase angle]
Tsuchinshan-ATLAS may be as bright as magnitude 5.2. Imagers in the southern hemisphere may be able to image the comet during nautical twilight in the morning. It is probably still too faint and close to the Sun for visual observation.
September 20 [0.44 au from the Sun, 1.23 au from Earth, 19 deg solar elongation, 50 deg phase angle]
The comet rises at the start of morning astronomical twilight from mid-latitudes in the southern hemisphere. At magnitude 4.5, it should be visually observable for those with a clear, flat horizon. It won’t rise until well into nautical twilight for observers at northern mid-latitudes.
September 25 [0.40 au from the Sun, 1.03 au from Earth, 22 deg solar elongation, 75 deg phase angle]
Tsuchinshan-ATLAS is at its highest in the morning sky for southern mid-latitude observers. Still, “highest” means it will only be 2 degrees above the horizon at the start of astronomical twilight and 8 degrees at the start of nautical twilight. The comet should be around magnitude 3.6.
September 27 [0.39 au from the Sun, 0.94 au from Earth, 22 deg solar elongation, 87 deg phase angle]
Tsuchinshan-ATLAS is at perihelion and magnitude 3.2. Conditions from the southern hemisphere are similar to those on the 20th. The comet should be bright enough to be imaged from the northern hemisphere, but visual observations may still not be possible.
September 29 [0.39 au from the Sun, 0.85 au from Earth, 22 deg solar elongation, 100 deg phase angle]
Tsuchinshan-ATLAS is at its highest in the morning sky for northern mid-latitude observers. Still, it doesn’t rise before the start of twilight and is only 3 degrees at the start of nautical twilight. Tsuchinshan-ATLAS is around magnitude 2.7. Though now past perihelion, the comet is rapidly brightening due to a decreasing Earth-comet distance and increasing phase angle. In the next few days, we will see observability as a contest between a lower altitude and brighter sky, but also a brighter comet.
Comets Between Magnitude 6 and 10
13P/Olbers
Discovered visually on 1815 March 6 by Heinrich Olbers in Bremen, Germany
Halley-type comet
Orbit (from Minor Planet Center, MPEC 2024-Q42)
13P/Olbers
Epoch 2024 Oct. 17.0 TT = JDT 2460600.5
T 2024 June 30.04994 TT Rudenko
q 1.1754681 (2000.0) P Q
n 0.01423818 Peri. 64.41676 -0.60853213 -0.37163125
a 16.8590520 Node 85.84708 +0.18555929 -0.92570126
e 0.9302767 Incl. 44.66599 +0.77152861 -0.07047968
P 69.2
From 1876 observations 2023 Oct. 8-2024 Aug. 25, mean residual 0".5.
Nongravitational parameters A1 = +0.65, A2 = -0.3232.
Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)
13P/Olbers Max El
(deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2024-Sep-01 13 18 +18 49 1.505 2.140 39E Com 8.2 18 5
2024-Sep-06 13 34 +16 15 1.550 2.198 38E Com 8.4 18 5
2024-Sep-11 13 48 +13 45 1.597 2.260 38E Boo 8.7 17 5
2024-Sep-16 14 02 +11 22 1.645 2.326 37E Boo 9.0 16 5
2024-Sep-21 14 15 +09 06 1.694 2.395 36E Boo 9.3 15 4
2024-Sep-26 14 28 +06 56 1.743 2.467 35E Vir 9.5 14 3
2024-Oct-01 14 40 +04 54 1.794 2.541 33E Vir 9.8 13 2
2024-Oct-06 14 51 +02 59 1.845 2.616 31E Vir 10.1 12 1
Comet Magnitude Formula (from 1956 ICQ and 2023 ALPO data)
m1 = -0.9 + 5 log d + 32.9 log r [Up through T-120 days]
m1 = 3.9 + 5 log d + 16.6 log r (T – 8)[After T-120 days]
where “T” is date of perihelion, “d” is Comet-Earth distance in au, and “r” is Comet-Sun distance in au
13P/Olbers is one of two returning Halley-type comets expected to be brighter than magnitude 12 this month. Last at perihelion in 1956, this year’s return saw perihelion on 2024 June 30 at 1.18 au and a peak brightness of magnitude 6.5 reached in July.
September sees Olbers as a low evening object, especially from the southern hemisphere, as it moves through Coma Berenices (Sep 1-6), Boötes (6-24), and Virgo (24-30). Since it is past perihelion, its distance from the Sun and Earth is increasing, resulting in a steady fade from around magnitude 8.2 on the 1st to 9.8 at the end of the month.
Photo Opportunities
Sep 01 - 13P/Olbers within a degree or so of the bright globular cluster pair M53 and NGC 5053
Sep 30 - 13P/Olbers passes within 20’ of 10th mag galaxy NGC 5701
Comets Between Magnitude 10 and 12
12P/Pons-Brooks
Discovered visually on 1812 July 12 by Jean-Louis Pons and rediscovered visually on 1883 September 2 by William R. Brooks
Halley-type comet
Orbit (from Minor Planet Center, MPEC 2024-Q42)
12P/Pons-Brooks
Epoch 2024 Oct. 17.0 TT = JDT 2460600.5
T 2024 Apr. 21.12533 TT Rudenko
q 0.7808584 (2000.0) P Q
n 0.01381092 Peri. 198.99348 +0.14509852 -0.32930545
a 17.2049860 Node 255.85512 +0.98567050 +0.13009697
e 0.9546144 Incl. 74.19215 +0.08602381 -0.93521800
P 71.4
From 1242 observations 2024 Feb. 1-Aug. 21, mean residual 0".6.
Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)
12P/Pons-Brooks Max El
(deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2024-Sep-01 12 20 -47 23 2.274 2.607 59E Cen 10.5 0 34
2024-Sep-06 12 36 -47 28 2.337 2.708 58E Cen 10.7 0 33
2024-Sep-11 12 52 -47 30 2.398 2.810 56E Cen 10.9 0 31
2024-Sep-16 13 06 -47 32 2.459 2.912 53E Cen 11.0 0 30
2024-Sep-21 13 20 -47 32 2.520 3.014 51E Cen 11.2 0 28
2024-Sep-26 13 33 -47 32 2.580 3.114 49E Cen 11.4 0 26
2024-Oct-01 13 46 -47 32 2.640 3.214 47E Cen 11.6 0 24
2024-Oct-06 13 58 -47 32 2.700 3.311 45E Cen 11.7 0 23
Comet Magnitude Formula (from ALPO and COBS data for the 1954 and 2023 returns)
m1 = 6.8 + 5 log d + 11.6 log r [between T-684 and T-275 days]
m1 = 4.2 + 5 log d + 9.7 log r [between T-275 days and perihelion]
m1 = 4.7 + 5 log d + 10.3 log r [after perihelion]
where “t” is date of perihelion, “d” is Comet-Earth distance in au, and “r” is Comet-Sun distance in au
The other returning Halley-type comet is 12P/Pons-Brooks, which is four months from its perihelion in late April at 0.78 au from the Sun. As September begins, the comet has already receded to a distance of 2.3 au from the Sun and 2.6 au from Earth.
This month, Halley-type comet 12P/Pons-Brooks fades from around magnitude 10.5 to 11.6. The comet is making its first return since 1954. Now past its April perihelion at 0.78 au, Pons-Brooks is receding back into the outer solar system. Its next perihelion will be in 71 years, in 2095.
The comet continues to be a southern-hemisphere-only object in Centaurus. Its path through Centaurus will provide one of the viewing/imaging highlights of the month as Pons-Brooks passes over the magnificent and bright globular cluster Omega Centauri (NGC 5139) on September 22-23.